1. The Algebraic Theory of Semigroups;Clifford,1961
2. Embedding theorems with amalgamation for semigroups;Howie,1962
3. Epimorphisms and dominions;Isbell,1966
4. Theorie der endlich erzeugbaren kommutativen Halbgruppen;Rédei;Hamburg. Math. Einzelschrift.,1963
5. Potential divisibility in commutative semigroups;Šutov;Izv. Vysshikh. Uchebn. Zavedenii Mat.,1964